The tired devil-in-our-midst formula takes on new vitality in this novel of a law firm headed by Satan himself. Neiderman ( Brainchild ) expertly carves a niche for evil within the gray areas of the legal profession when Kevin Taylor, basically nice but ambitious, finds himself on slippery moral ground in his aggressive defense of a schoolteacher guilty of sexually abusing her pupils. His sinister success nets him a position with the criminal law firm of John Milton and Associates, whose suave founder has a computer file marked ``futures,'' listing as-yet-uncommitted atrocities whose perpetrators will be represented by Milton's minions. Neiderman plants an obvious trail of clues to the hellish heart behind the firm's Edenic veneer, but the chillingly resonant ending drives home a stark homily--that selling one's soul is likely to be an irreversible transaction. (Mar.)